1. Field of the Invention
The present invention relates to a window glass antenna device for use on an automobile, for example, and more particularly to a window glass antenna device having an antenna in the form of defroster heater wires in a window glass panel of an automobile.
2. Description of the Relevant Art
Japanese laid-open utility model publication No. 63-129307 discloses a window glass antenna device having an antenna which comprises a plurality of defroster heater wires in a window glass panel of an automobile. The defroster heater wires have respective ends electrically connected to a bus bar, from which received radio signals can be transmitted through a DC blocking capacitor.
Since the defroster heater wires are used as antenna elements, the DC blocking capacitor is required to block a current which is supplied to heat the defroster heater wires.
FIG. 1 of the accompanying drawings shows such a prior window glass antenna device with a plurality of defroster heater wires as antenna elements. The illustrated conventional window glass antenna device, generally denoted at 100, has defroster heater wires 104 having ends connected to bus bars 101, 102 and opposite ends connected to a bus bar 103. The bus bar 103 is connected through a DC blocking capacitor 110 to a radio receiver (not shown). The bus bars 101, 102 are connected respectively to choke coils 106, 105 that are connected to respective terminals of a capacitor 107. The capacitor 107 is connected through a switch 108 to a DC power supply 109. When the switch 108 is closed, DC electric energy is supplied from the DC power supply 109 through the switch 108 and the choke coils 105, 106 to the defroster heater wires 104. The choke coils 105, 106 serve to provide a sufficiently high impedance in the frequency range of received radio waves as viewed from the defroster heater wires 104. The capacitor 107 serves to prevent power supply noises from being transmitted to the defroster heater wires 104.
In the case where the defroster heater wires 104 are disposed between glass layers of a laminated window glass panel 111, which is typically a rear window glass panel, it is necessary that the bus bars 101, 102, 103 be connected to outer terminals through copper foil or the like. However, the process of manufacturing such a window glass antenna device is complex and time-consuming because connecting the bus bars 101, 102, 103 to outer terminals through copper foil or the like requires a number of manufacturing steps.